<?php
session_start();
?>
<form action="" method="post">
<p>Enter text shown below:</p>
<p><img src="./" alt="" /></p>
<p><input type="text" name="keystring" /></p>
<p><input type="submit" value="Check" /></p>
</form>
<?php
if ( count($_POST) > 0 ) {
	if ( isset($_SESSION['captcha_keystring']) && $_SESSION['captcha_keystring'] === $_POST['keystring'] ) {
		echo "Correct";
	} else {
		echo "Wrong";
	}
}
unset($_SESSION['captcha_keystring']);
?>